The present invention relates to a tensioner for tensioning a belt or chain adequately by using an urging tension rod. More particularly, the present invention relates to such a tensioner which has a compression spring acting to operate the urging tension rod.
This type of tensioner is used to prevent a number of problems. When a tension rod is excessively urged due to the excessive variation of driving torque, the belt or chain becomes excessively tensioned. Sometimes as a result, buzzing or excessive wear on the belt or chain can result. Taking this undesirable situation into consideration, a tensioner has been disclosed by the Japanese Utility Model Application Laid-open No. 62-13257 in which the tension rod has been provided with a restoring capacity.
As shown in FIG. 7 of the present application, the tension rod 101 of a conventional tensioner ratchet 100 for tensioning a chain is mounted in a casing 104 so as to be urged freely by a compression spring 105. The tension rod 101 is provided with a rack portion on its side, and mating teeth of ratchet pawl 102 engage with the rack portion. A shaft 103, fixed on the ratchet pawl 102, is inserted in the vertical slot 106 so that the teeth of the ratchet pawl may slip on the rack to change its position. When the chain is slackened, normally, the tension rod 101 advances to keep adequate tension on the chain. The returning stroke of tension rod 101 is controlled by the ratchet pawl 102. On the other hand, when the chain is excessively tensioned, due to an excessive advance of tension rod 101, the shaft 103, fixed on the ratchet pawl 102, works to alleviate excessive tension.
Hereinafter, the problems to be solved by the invention will be explained. Since the back stroke of tension rod 101 is controlled by the ratchet pawl 102, the shaft 103 and vertical slot 106 as aforementioned, the back stroke of the tension rod 101, which has been excessively urged by the resonant amplitude of the tensioned belt or chain is terminated when the shaft 103 of ratchet pawl hits on the bottom of vertical slot 106 after coursing the full length of the slot, the tension rod 101 does not function to alleviate excessive tension of chain or belt because the tensioner only uses a regid object against the counterforce of the tensioned belt or chain.
The present invention has been developed considering the above situations and provides a tensioner having a prompt response to slackening, which functions to alleviate excessive tension on the belt or chain and which has a simple and compact construction.